1. Field of the Invention
The present invention relates to an optical pickup device, an information reproduction/recording apparatus, and an information processing apparatus.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 11-162003 discloses an information reproduction apparatus that reproduces information recorded on an optical disk. In this information reproduction apparatus, light is emitted on the optical disk, and the reflection light from the optical disk is divided and received by a plurality of light receiving members. The current signals obtained from the respective light receiving members are added by an adder, and the resultant signal is then converted into a voltage by a current/voltage converter (hereinafter referred to as xe2x80x9cI/V converterxe2x80x9d).
In accordance with the technique, an amplifier is mounted in the same package as the light receiving members. Since the I/V converter is also mounted on the optical pickup apparatus, a reproduction signal of the optical disk can be resistant to an adverse influence from noise, because it can be extended by 20 cm or more by a voltage signal that is relatively resistant to noise.
The adder that adds up the output signals of the respective light receiving members is also mounted on the optical pickup apparatus. In view of this, an adverse influence from noise can be avoided. In a case where the voltage signals converted from the output signals of the light receiving members are transmitted over a long distance through a plurality (four, for instance) of signal lines, with the noise superimposed on each signal line being N, the noise superimposed on the voltage signal after the adding operation by the adder is Nxc3x97{square root over ( )}4=2xc3x97N. On the other hand, after the voltage signals are added up in the optical pickup apparatus, the resultant voltage signal is outputted to the circuit substrate through a signal line, so that the superimposed noise can be equivalent to N.
In the method disclosed in Japanese Laid-Open Patent Application No. 11-162003, however, there are problems with the dynamic range of the circuit. More specifically, since the RF signal is an addition signal of the output signals of the light receiving members, the RF signal has a signal level that is several times (four times in a case of a general optical system, because the four light receiving members are divided from one light receiving element) higher than the output of each of the light receiving members. Accordingly, even if the output range of the RF signal is set in the entire dynamic range, the range of the output signal of each of the light receiving members is limited to one fourth of the dynamic range. Since the output of each of the light receiving members is normally used for generating a servo signal for controlling the operation of the pickup device, it has a low bandwidth, and is relatively resistant to noise. However, with a larger number of light receiving members or a higher reading rate of the optical disk, the servo signal might be adversely influenced by noise.
When information is to be recorded on a DVD-R disk, for instance, the quantity of light for forming recording marks equivalent to xe2x80x9c1xe2x80x9d is more than 10 times as large as the quantity of light for recording spaces equivalent to xe2x80x9c0xe2x80x9d. To prevent saturation of the output of the RF signal for the large quantity of light for forming the recording marks, the dynamic range of the output of each of the light receiving members during the space recording operation is only {fraction (1/40)} of the RF signal. As a result, the output signal of each of the light receiving members is limited to an extremely narrow range.
Furthermore, there is another problem with the prior art. To restrict the noise on a signal line that serves as a transmission path, a signal that has the opposite polarity to the RF signal is transmitted at the same time as the RF signal (the differential output), and the difference is removed at the receiving end, so as to remove the noise in the in-phase component superimposed on both signals. Throughout this specification, the complementary signal for the RF signal is referred to as xe2x80x9cRFxe2x88x92xe2x80x9d. In a general differential output operation, if the RF signal is a signal on the positive side with respect to a predetermined reference voltage Vref, the RFxe2x88x92 is a signal obtained by inverting the RF signal about the reference voltage Vref. As a result, the RFxe2x88x92 has the opposite polarity to the RF signal. Alternatively, when the outputs of the respective light receiving members are added up, the outputs of the light receiving members are inverted at the same time. In this example, the output voltage of RFxe2x88x92 is situated on the negative side with respect to the reference voltage Vref. As a result, there is a problem that a twice as wide dynamic range is required.
It is a general object of the present invention to provide optical pickup devices, information reproduction/recording apparatuses, and information processing apparatuses, in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an optical pickup device in which the signals outputted from the light receiving members are converted into voltage signals and added up, and the resultant addition signal is resistant to noise, by fully utilizing the dynamic range.
Another specific object of the present invention is to provide an optical pickup device in which the signals outputted from the light receiving members are converted into voltage signals and then added up, and in-phase noise is removed from the resultant addition signal and its complementary signal, without widening the dynamic range.
Yet another specific object of the present invention is to realize the removal of in-phase noise at a low production cost.
Still another specific object of the present invention is to perform the removal of the in-phase noise, using a complete complementary signal, without causing a signal delay.
The above objects of the present invention are achieved by an optical pickup device that comprises:
a light source that emits light onto an object;
a plurality of light receiving members that receive divided reflection light from the object; and
a signal processing circuit that converts a current signal outputted from each of the plurality of light receiving members into a voltage signal, performs an adding operation on the voltage signals, and performs attenuation on the added voltage signal.
With this optical pickup device, the dynamic range is limited so as to prevent the signal level of each signal from becoming too small. Thus, the signals outputted from both the light receiving members and the signal processing circuit can be resistant to an adverse influence from noise, fully utilizing the dynamic range. The attenuation is carried out in such a manner that the signal obtained by converting the output signals of the light receiving members into the voltage signals, adding the voltage signals, and attenuating the added voltage signal has substantially the same level as the signal obtained by converting the output signal of a single light receiving member into a voltage signal.
The above optical pickup device further comprises a complementary signal generating circuit that generates a complementary signal of the added voltage signal by attenuating a signal that has a waveform symmetrical to the added voltage signal about a predetermined reference voltage.
Accordingly, the in-phase signal of the signal outputted from the signal processing circuit can also be resistant to an adverse influence from noise, thus fully utilizing the dynamic range.
The above objects of the present invention are also achieved by an optical pickup device that comprises:
a light source that emits light onto an object;
a plurality of light receiving members that receive divided reflection light from the object;
a signal processing circuit that converts a current signal outputted from each of the plurality of light receiving members into a voltage signal, and performs an adding operation on the voltage signals; and
a complementary signal generating circuit that generates a complementary signal of the added voltage signal by performing a predetermined level shift on a signal that has a waveform symmetrical to the added voltage signal about a predetermined reference voltage.
With this optical pickup device, the difference in signal level between the signal outputted from the signal processing circuit and its complementary signal is small. Thus, the in-phase noise can be removed from the signal outputted from the signal processing circuit and its complementary signal, without widening the dynamic range.
In the above optical pickup device, the signal processing circuit comprises:
a plurality of I/V converters, each of which converts the current signal outputted from each corresponding one of the light receiving members into the voltage signal; and
an adder that adds up the voltage signals, and
the complementary signal generating circuit comprises:
an inversion circuit that receives the added voltage signal outputted from the signal processing circuit, and generates the signal that has the waveform symmetrical to the added voltage signal about the predetermined reference voltage; and
a shift circuit that generates the complementary signal by performing the predetermined level shift on the signal generated by the inversion circuit.
With this optical pickup device, the complementary signal generating circuit constituted by the inversion circuit and the shift circuit generates a complementary signal, using the output signal of the signal processing circuit. Thus, the number of circuit components in the complementary signal generating circuit can be reduced, and the production cost of the optical pickup device can be lowered.
In the above optical pickup device, the signal processing circuit comprises:
a plurality of I/V converters, each of which converts the current signal outputted from each of the light receiving members into the voltage signal; and
an adder that adds up each voltage signal, and
the complementary signal generating circuit comprises:
an inversion adder that generates the signal having the waveform symmetrical to the added voltage signal about the predetermined reference voltage; and
a shift circuit that generates the complementary signal by performing the predetermined level shift on the signal generated by the inversion adder.
With this optical pickup device, the difference in number of circuit components is small between the signal processing circuit and the complementary signal generating circuit. Accordingly, a delay of the complementary signal becomes shorter, making the complementary signal more complete.
In the above optical pickup device, the signal processing circuit further performs an attenuation operation on the added voltage signal; and the complementary signal generating circuit comprises an attenuator that attenuates the complementary signal.
With this optical pick up device, the level of the signal outputted from each of the light receiving members can be prevented from becoming too small. Thus, the signals outputted from both the light receiving members and the signal processing circuit can be resistant to noise, fully utilizing the dynamic range.
The above objects of the present invention are also achieved by an information reproduction/recording apparatus that can optically perform either one or both of information reproduction and recording on a recording medium, said apparatus comprising:
an optical pickup device that includes a light source for emitting light onto the recording medium, and a plurality of light receiving members that receive divided reflection light from the recording medium;
a moving device that moves the optical pickup device;
a detector unit that detects an irradiation spot of the light on the recording medium;
a control unit that controls the irradiation spot to follow a read or write position on the recording medium based on a result of the detection by the detector unit; and
a reproduction unit that is disposed independently of the optical pickup device, and is connected to the optical pickup device by a transmission path for transmitting and receiving a voltage signal outputted from a signal processing circuit and a complementary signal generating circuit, so as to reproduce information stored in the recording medium based on the voltage signal outputted from the signal processing circuit.
With this information reproduction/recording apparatus, the same effects as with the above-described optical pickup device can also be achieved.
The above objects of the present invention are also achieved by an information processing apparatus provided with the above-described information reproduction/recording apparatus, in which various information processing operations can be performed.
With this information processing apparatus, the same effects as with the above-described information reproduction/recording apparatus can also be achieved.
Other objects and further features of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.